Patches are known that comprise a backing sheet coated on one face in a reservoir-forming layer known as a "matrix", containing one or more active substances for diffusing into the skin and/or for acting thereon.
The invention relates more particularly to a patch in which the matrix is made of a material that has intrinsic adhesive properties.
Selecting this material gives rise to difficulties, in particular:
it must be capable of containing the active substance(s) for acting on the skin; PA1 its adhesion to the skin must not be too strong, particularly if it is to be applied in repeated manner, since otherwise the region of the body on which the patch is applied will become irritated and removing the patch will become painful; PA1 its adhesion must not be too weak either, since otherwise it will not be able to adhere to the skin if it is moist or if it becomes moist, e.g. because of sweating; PA1 it must be sufficiently flexible to allow the patch to fit over the shape of the region of the body on which it is applied; PA1 it must remain on the backing sheet when the patch is removed; and PA1 finally, it must make it possible to extract the impurities that are to be found on the surface of the skin, in particular sebum or sweat. PA1 a reflecting layer that reflects the infrared radiation released by the human body, and between said reflecting layer and said face for application to the skin: PA1 a matrix made of a material having self-adhesive properties and comprising at least an acrylic or vinyl polymer whose adhesive properties increase with temperature over the range 20.degree. C. to 40.degree. C.; and PA1 in said matrix at least one active substance having an effect on the skin. PA1 significantly increase the temperature of the matrix, and given the particular material selected for making it, reinforce its adhesion to the skin; PA1 enhance diffusion of the active substance(s) within the matrix; and PA1 increase blood circulation beneath the patch, which can be favorable to the penetration and/or action of said active substances.
In spite of these difficulties, several materials have been proposed for making the matrix, however they are not necessarily suitable for all of the active substances that it might be desirable to incorporate therein.
French patent 2 738 744 or European patent 0 309 309 teach in particular the use of hydrophobic or hyposoluble materials for constituting the matrix.
The hydrosoluble material described in European patent 0 309 309 is relatively impractical in use since it does not present the required adhesive properties prior to application to the skin and it requires the skin to be previously moistened.